Centrifugal pump

ABSTRACT

A centrifugal pump pumps fluid containing large or long objects of solid material. Solid parts cause problems with centrifugal pumps in that they both stick to the edge of the vanes of the pump wheel and get in between the pump wheel and the housing and stick to either one of these may cause the pump wheel to slow down or get stuck. Large parts may also form a bridge between two vanes. Objects which have become stuck to and rotate together with the pump wheel easily gather more objects and growth of the aggregate is often very rapid. In all of these cases the flow through the pump is distributed and the capacity of the pump is reduced. These problems are avoided with a centrifugal pump in which the edges of the vanes ( 11, 12, 13, 14 ) extend themselves continuously in the direction of the flow from the input adjacent the shaft and at an acute angle thereto to a lower part close to the wall ( 1 - 1 A) of the housing and forwards in the direction of the flow of the pumped fluid.

RELATED APPLICATIONS

This application is the national phase of international applicationPCT/SE99/01170 filed Jun. 29, 1999 which designated the U.S, and thatinternational application was published under PCT Article 21(2) inEnglish.

BACKGROUND OF THE INVENTION

The present invention refers to a centrifugal pump for fluids containinglarge or long solid objects. Primarily this means wooden chips, textile-and fibre parts, plastic and other solid pieces in the size order of5-150 mm. Pumps according to the invention are especially intended forpumping of liquid which has a large content of solid material which maybe up to about 50%.

PRIOR ART PROBLEMS

Solid objects cause problems when pumping with centrifugal pumps in thatthey both stick on the edges of the vanes of the pump wheel and forcetheir way in between the pump wheel and the housing and get stuck toeither one of these where they may cause the pump wheel to slow down orget stuck. The larger objects may also bridge between two vanes. Objectswhich have stuck and rotate together with the pump wheel easily gathermore objects and the aggregate often grows rapidly. In all cases theflow through the pump is disturbed and its capacity is reduced. Whensuch problems occur the pump has to be stopped and cleaned which oftenbrings with it a stop for the entire process in which the pump isincluded.

OBJECTS OF THE INVENTION

The present invention is for a centrifugal pump in which the abovementioned drawbacks are avoided. The object of the present invention isa pump of the above mentioned kind such that as far as possible it isavoided that solid objects stick to the pump wheel or housing. It isanother object of the invention to achieve release of stuck objects assoon as possible without having to stop the pump or take any otherspecial action.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below with reference to exemplary embodimentswhich are shown in the enclosed figures, in which:

FIG. 1 is a cross-section of a pump according to the invention.

FIGS. 2 and 3 are respectively a cross-section and front view of a pumpwheel of a pump according to the invention.

FIG. 4 is a cross-section of some parts of the pump of FIG. 1.

FIG. 5 is an enlarged view of a portion of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The pump shown in FIG. 1 has a conventionally designed housing 1 inwhich there is a pump wheel 2 which is connected to a driving shaft 10.In the embodiments shown in the figures the pump wheel has four vanes11, 12, 13 and 14. The housing of the pump has an inner lining or weardisc 1A the inside of which is adapted to the shape of the vanes of thepump wheel. At the back of the pump wheel the housing comprises a pumpcover 17. Bearing and sealing of the pump shaft is made in known manner.

In prior art pumps the vanes extend along the wear disc 1A (upwards inthe lower half of FIG. 1) and end approximately along the broken line 3.In centrifugal pumps according to the invention the vanes extendthemselves considerably farther towards the inflowing fluid, so that theedge of the vane which is closest to the outlet follows the inside weardisc 1A and continuously extends itself up to an extension of the shaft10 and, in a plane in the direction of the pump shaft, is at an acuteangle therewith. Long large objects can not stick to the front edges ofthe vanes but are directed into the pump wheel in a direction whichgenerally coincides with the direction of the flow thus eliminating therisk of bridging between two adjacent vanes. Preferably the vanes alsoare at an acute angle to the shaft of rotation in a vertical plane atright angle to the plane which is shown in the figure.

In some applications the pump wheel also has an intermediate vane inorder to attain the required pressure during pumping. Such anintermediate vane 18 is shown in FIG. 2 from which is apparent that itstarts some distance outwards on the pump wheel from its hub. The edgeof the intermediate vane 18 slopes from the starting point slightlyupwards from the plane of the pump wheel until it has the same height asthe other, larger vanes 11, 12, 13, 14. From this point and on to theperiphery of the pump wheel the intermediate vane 18 has mainly the sameshape as the other vanes. The number of intermediate vanes is in mostcases the same as the number of the other vanes. By this arrangement ofthe intermediate vanes it is achieved that solid particles do not stickto the intermediate vanes but are thrown at the wear disc 1A in the sameway as at the other, larger vanes.

At the inside of the wall of the housing 1-1A there are one or moregrooves 4, 16. The grooves extend themselves from the outer outletchannel in the housing along the whole of the part of the wall adjacentto the vanes and some distance further.

Objects of a size such that they may get into the slit between a vaneand the housing are hooked by the grooves 4, 16 and ground to pieces.The slit 5, 15 between a vane and the housing is so designed that it, atleast at an end section thereof, widens in the direction of the flow andtowards the periphery of the pump wheel as shown in FIG. 5. Due to thisdesign all particles which get in between a vane and the housing areground and conveyed out with the fluid flow.

The pump wheel may also have back side vanes 6, 8. In this case also thecover 17, which is facing the back of the pump wheel, has one or moregrooves 7, 9. This brings with it that solid objects which get inbetween the pump wheel and the cover are ground when they are hooked bythe grooves 7, 9 and hit by the back side vanes 6, 8. The slit betweenthe pump wheel and the cover preferably widens continuously outwardsfrom the shaft in order to make it easier for objects which have gotinto the slit to get out to the outlet channel.

Further embodiments of the centrifugal pump are possible within theframework of the inventive idea. The grooves both in the housing and thecover of the pump may in other embodiments of the invention be replacedby ridges or similar edges at the housing and the cover. The grooves orridges may then form a straight or bent line along the surface at whichthey are positioned. They also ought to have a rounded bottom or outsideto facilitate the loosening of temporarily stuck objects. The front partof the vanes may together with the corresponding part of the shaft be aseparate addition to conventional pump wheels.

What is claimed is:
 1. A centrifugal pump for pumping of liquidcontaining large solid parts, comprising: a pump wheel having a shaftand vanes, a pump housing having an inner lining or wear disc having aninside adapted to a shape of said vanes, said vanes having edgesextending continuously upstream from a point adjacent the lining or weardisc to said shaft forming an acute angle to said shaft, and betweensaid pump housing and outer edges of said vanes, at least in a rear partthereof as seen in a flow direction, there being a slit (5, 15) whichwidens in said flow direction.
 2. A centrifugal pump according to claim1 wherein the housing has one or more grooves (4, 16) at a side whichfaces the edges of the vanes.
 3. A centrifugal pump according to claim 2wherein the housing has one or more ridges on a surface which faces saidvanes.
 4. A centrifugal pump according to any one of the precedingclaims wherein the pump wheel has rear vanes (6, 8) and one or moregrooves (7, 9) or corresponding ridges are arranged in or at the cover(17) of the housing.